To use PHP_LSAPI_CHILDREN, just set it as a environment variable to match "Max Conn" value, set "instances" to 1.
The benefit of doing this is that all PHP processes sharing the same block of memory for the opcode cache, but all PHP processes will be started statically, not on demand. Performance wise, you may not notice big differences.

We are working on a PHP LiteSpeed SAPI module which will start PHP children processes on demand and only use one memory block for the opcode cache. Stay tuned.